查看更多>>摘要：? 2021 Elsevier B.V.The porosity of plasma electrolytic oxidation (PEO) coating limits PEO technology for improving the corrosion resistance of magnesium (Mg) and its alloys. In this study, we innovatively added double magnetic to the PEO process and explored the effects of magnetic field force (MFF) in the process of particle formation in electrolytes, growth of PEO coating on Mg, and coating growth at arcing stage only. Results indicated that MFF greatly improved mixed composition in electrolytes adequately and evenly, reducing the energy of PEO coating formation by increasing the conductivity of the electrolyte, thereby reducing the breakdown voltage, and then reducing porosity (decreasing from 17.52% to 0.58%) and contact angle of PEO coatings. Compared with the nonmagnetic action group, the corrosion current density of the MFF group is decreased by one order of magnitude. The lower porosity would inhibit infiltration of the corrosive medium into the inner regions of the coating and subsequently down to the substrate, thus improving the corrosion resistance of the coating. Mg with PEO coatings prepared under MFF for a long time degrades less than uncoated and other coatings, which makes them more suitable for orthopedic implants.
查看更多>>摘要：? 2022In order to investigate the morphology and size effect of Pd nanocrystals on gas sensing performance of SnO2, Pd nanocrystals with different sizes (3, 20, 50 nm) and morphologies were synthesized and a series of Pd-SnO2 composites were prepared by decorating Pd nanoparticles (PdNP, ~3 nm), Pd nanocube (PdNC1, ~20 nm), Pd nanocube (PdNC2, ~50 nm), Pd rhombic dodecahedron (PdRD, ~50 nm), Pd octahedron (PdOC, ~50 nm) on the surface of SnO2 nanosheets. The test results showed that all Pd-SnO2 sensors exhibited dual selectivity to H2 at 200 °C and HCHO at 260 °C. In all Pd-SnO2 composites with different sizes of Pd, 2%PdNP-SnO2 sensor exhibited the best sensing performance. In all Pd-SnO2 composites with different shapes of Pd but similar size, PdNC1-SnO2 and PdOC-SnO2 sensors exhibited better sensing performance to HCHO and H2, respectively. Pd-SnO2 composites showed Pd shape and size-dependent sensing performance, and the size effect is more significant than morphology effect. Size effect is ascribed to the smaller size with more active sites and PdO species, and shape effect is attributed to the different adsorption energies of different facets to HCHO, which is proved by DFT calculation. In addition, the improved performance of SnO2 can be ascribed to two aspects: one is the suitable catalytic activity of Pd to HCHO and H2 oxidation; the other is that the transformation of Pd?PdO in air and HCHO or H2 leads to a large resistance change of SnO2.
查看更多>>摘要：? 2022Although laser surface remelting displays excellent potential for repairing the nickel-based single crystal (SX) superalloy components, controlling the grain structure while avoiding the stray grain (SG) formation is still a challenge in the industry. In order to inhibit SG formation for nickel superalloys, a novel rotated laser irradiation approach is introduced in this paper and the study of the origin of the SG formation in laser directed solidification process. Besides, a numerical model of combined alloy composition with the tendency of equiaxed grain formation during epitaxial growth processing was developed in this paper to reveal the mechanism of SG formation at the bottom of the molten pool. Results indicate that SGs formed at the bottom of the molten pool are mainly due to the remarkably increased possibility of the equiaxed grain transformation with the rough fusion interface. During the laser process, the number of SGs gradually decreases with the increase of the angle (θ) between the laser irradiation and gravity direction. For θ = 90°, well-aligned epitaxial growth of [001] dendrites without any SGs are observed in the pool with the smooth fusion interface. Furthermore, applying the new laser deposition technique based on this phenomenon during laser directional solidification will be an effective method to control the grain-oriented growth in industrial manufacture for the single crystal components.
查看更多>>摘要：? 2022Metal-organic frameworks (MOFs) have ordered porous structure and intriguing properties for supercapacitors, however, poor conductivity and cycle stability limits their application. To solve these problems, hence, a simple strategy is proposed, by which MOFs are in-situ grown in the porous conductive p-MXene substrate. And then, along with the introduction of CuS, the grown Ni-MOF is derived to Ni3S4, which is more stable and more electrochemically active. Due to higher contact area, excellent synergistic effect and more exposed active sites, the prepared sandwiched p-MXene@Ni3S4/CuS nanostructure displays a big specific capacitance (1917 F·g?1) and superior cycling performance (91.2%@30000). What's more, the assembled p-MXene@Ni3S4/CuS//AC asymmetric device delivers a high energy density of 87.62 Wh·Kg?1 at the power density of 775.02 W·Kg?1, suggesting that this material provides a brilliant candidate for energy storage.
查看更多>>摘要：? 2022Metasurface-based devices are utilized to achieve high absorption in the determined frequency band and applied in sensing. The dielectric properties of vanadium dioxide (VO2) are sensitive to ambient temperature. The development of metasurface devices based on the tunable of VO2 has attracted a lot of attention. In this work, a tunable metasurface based on the VO2 layer is proposed and verified in the terahertz (THz) band. An absorption peak at 7.71 THz at room temperature is achieved based on the coupling effect between bright modes. This absorption peak is enhanced by optimizing the lattice constant of the unit cell (P) or metal particle diameter (D) in experiments. As the parameter P increases, the absorption peak is strengthened and moved to higher frequencies. Conversely, when the parameter D is increased, this absorption peak is moved to lower frequencies. An LC mode is suggested to reveal the influence of the structural parameters (P, D) on the absorption properties. Two measured figure of merit (FOM) (19.4, and 29) are obtained based on liquid sensing at room temperature. Since the resonance property of the VO2 layer is temperature reversible, the absorption performance of the metasurface is repeatable in the heating and cooling process. In the final experiments, the absorption peak is controlled in the heating and cooling process. Such a metasurface can be applied in liquid and temperature sensing.
查看更多>>摘要：? 2022 Elsevier B.V.The high strength, ductility, and corrosion resistance of alloys are highly desirable functional materials for biomedical applications. Multi-component alloys with a single face-centered-cubic (fcc) phase structure can provide superior ductility, while microstructures such as twins and stacking faults (SF) can be incorporated into the matrix to improve the strength of the alloy without damaging plasticity. Here, we have developed a single-fcc phase alloy Co36Fe36Cr18Ni10 with low stacking faults energy, which can effectively produce annealed twins by recrystallization annealing after cold rolling. The microstructure and mechanical properties of Co36Fe36Cr18Ni10 compared to commercial 316L alloy was methodically investigated by EBSD, TEM, and tensile testing. The results reveal that the Co36Fe36Cr18Ni10 alloy contains more twin boundaries and a high density of nano-twins and SFs in the microstructure, which effectively improve the strength of Co36Fe36Cr18Ni10 alloy meanwhile maintaining a similar ductility to commercial 316L. The corrosion behavior of Co36Fe36Cr18Ni10 and 316L in simulated body fluids has been investigated using electrochemical characterization, indicated that compared to 316L ss, pitting in Co36Fe36Cr18Ni10 alloys is easily inhibited and rapid re-passivation, meanwhile the twin boundaries were effective in weakening the formation of corrosion pits and impeded the expansion of corrosion crack. Compare the surfaces of the two alloys after passivation, apart from the Cr2O3/Cr(OH)3 contained in the passive film, the interactions between Co and other components in the passivation film produce more indissoluble substances with a lower enthalpy of formation that will enhance the passive film stability of Co36Fe36Cr18Ni10 alloy.
查看更多>>摘要：? 2022 Elsevier B.V.The mechanical properties and microstructure of 2050 Al-Li alloy during non-isothermal aging (NIA) were investigated. The research results show that during the NIA heating stage (130 °C→220 °C), the strength of 2050 Al-Li alloy continues to rise. In the cooling stage (220 °C→130 °C), the strength of the alloy begins to decrease at 200 °C and reaches the minimum value at180 °C. When the temperature drops to 150 °C, the alloy strength reaches its maximum, and the yield strength (YS), ultimate tensile strength (UTS) and elongation are 544 MPa, 568 MPa and 9.8%, respectively. Microstructure studies have shown that during the heating stage of NIA, the volume fraction, average thickness and diameter of the T1 phase have been increasing. In the cooling stage, the average thickness and diameter of the T1 phase continue to increase, but the volume fraction begins to decrease. When the aging temperature drops to 190 °C, the average thickness and diameter of the T1 phase begin to decrease, but the volume fraction begins to increase. When it drops to 150 °C, the volume fraction of T1 phase, the average thickness and diameter are 8.7%, 2 nm and 26.5 nm, respectively. In addition, it is calculated that the critical thickness for the transformation of the T1 phase strengthening mechanism is 0.82 nm. Therefore, the main strengthening mechanism of the 2050 Al-Li alloy in the entire NIA treatment process is the Orowan bypass mechanism.
查看更多>>摘要：? 2022The separation mechanism of Si+TiSi2 eutectic alloy and Fe atom segregation were investigated during the electromagnetic directional solidification of Ti-80 wt%Si alloy melt at pull-down rates from 5 μm/s to 20 μm/s. The experimental results indicated that a fine lamellar Si+TiSi2 eutectic alloy was obtained in the middle of the ingot after electromagnetic directional solidification. Fe impurities were captured by primary SiC particles at the bottom of the ingot, which then segregated at the top of the ingot. When the pull-down rate was 5 μm/s, the solidification front was always close to the induction coil. Electromagnetic stirring produced forced convection that promoted Si+TiSi2 eutectic alloy precipitation by mixing the melt and offsetting the temperature gradient caused by the precipitation of the primary phase, thereby inhibiting segregation. Thus, the optimal pull-down rate for fabricating Si+TiSi2 eutectic alloy was 5 μm/s. At this pull-down rate, the maximum thickness of the Si+TiSi2 eutectic alloy layer was 27 mm, and the removal rate of impurity Fe in this layer reached 98.98%.
查看更多>>摘要：? 2022 Elsevier B.V.Memory effect of magnetoelectric (ME) coupling is observed in antiferromagnetic Co4Ta2O9 ME poling generated polarization below Néel temperature is retrieved after Co4Ta2O9 is warmed to paramagnetic phase and then cooled to antiferromagnetic phase without being poled. This effect is ascribed to polar nanoregions in paramagnetic phase due to short range magnetic ordering as evidenced by temperature dependent magnetic entropy. If the applied magnetic field in paramagnetic phase is weakened, the memory effect is strengthened, which is ascribed to the less change of spin alignment induced by the weaker magnetic field. If we switch this magnetic field, the polarization when reentering polar phase is also reversed. Furthermore, the memory effect is also reflected in electric field dependent magnetization after the second cooling process without being poled.
查看更多>>摘要：? 2022Co3O4 and nickel–cobalt layered double hydroxide (Ni-Co LDH) have been extensively studied as a typical cobalt-based pseudocapacitive materials. To further improve their electrochemical performance, the cobalt-based materials and carbon were integrated to prepare hierarchical Co3O4 @C@Ni-Co LDH nanoarrays through the hydrothermal and calcination methods. According to the characterization, the results show the Co3O4 nanocones with single-crystalline structure serve as the stable frameworks and the amorphous carbon coated on the Co3O4 nanocones improves the conductivity and the structural stability significantly. Moreover, numerous active sites of Redox reactions, provided by the Ni-Co LDH, improve specific capacitance of electrode. Based on performance measurements, it was illustrated that the integrated Co3O4 @C@Ni-Co LDH electrodes possessed the outstanding performance of specific capacitance (1755 F/g at 1 A/g) with remarkable cycling stability (specific capacitance remained at 90.47% after 5000 cycles at the current density of 10 A/g) because of the synergetic effects of high activity and conductivity Co3O4 @C scaffolds and well-defined Ni-Co LDH nanoneedles. The asymmetric supercapacitors, based on Co3O4 @C@Ni-Co LDH // active carbon, showed an extraordinary cyclic stability with the retention rate of specific capacitance is 94.47% after 16000 cycles. Furthermore, prepared devices showed the excellent energy density with 33.02 Wh/kg with the power density was 398.85 W/kg. The excellent electrochemical properties of Co3O4 @C@Ni-Co LDH electrodes indicate that the multi-component integrated materials have great theoretical significance for the study of high-performance electrode materials, and also reflect that the Co3O4 @C@Ni-Co LDH electrodes exhibit outstanding value and extremely promising prospect in practical application.
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